Digital single lens reflex cameras, with which an optical image of a subject is converted into an electrical image signal and outputted, have rapidly grown in popularity in recent years. With these digital single lens reflex cameras, when the user views a subject through the viewfinder, the light incident on the imaging lens (that is, the subject image) is reflected by a reflecting mirror disposed along the imaging optical path beyond the lens, which changes the optical path and sends the subject image through a pentaprism or the like to create a positive image, and guides this to an optical viewfinder. This allows the subject image that has passed through the lens to be seen through the optical viewfinder. Therefore, the position where the viewfinder optical path is formed usually becomes the home position of the reflecting mirror.
Meanwhile, when a lens is used for imaging, the reflecting mirror changes its position instantly and is retracted from the imaging optical path so that the viewfinder optical path is switched to the imaging optical path, and then instantly returns to its home position when imaging is over. With a single-lens reflex camera, this operation is the same regardless of whether the camera is a conventional silver halide camera or a digital camera.
One of the features of a digital camera is that imaging is performed while the user looks at a display device (such as a liquid crystal monitor), and the captured image can be checked right after it is captured. However, when a conventional single lens reflex reflecting mirror is used, a liquid crystal monitor cannot be used during imaging. Since imaging cannot be performed by using a liquid crystal monitor, the user has to look through the viewfinder during imaging, so conventional camera systems have been extremely difficult to use, especially for novices who are inexperienced in using digital cameras.
In view of this, there has been a proposal for a digital single lens reflex camera with which imaging can be performed while looking at a liquid crystal monitor.
Also, with a digital single lens reflex camera, phase difference detection is generally employed as the focus point detection method (see Patent Citation 1, for example).    Patent Citation 1: Japanese Laid-Open Patent Application 2006-3417